1. Field of the Invention
The present invention relates to a method, a system, an apparatus and a program each of which programs defect data for evaluation of a reticle inspection apparatus and performs sensitivity evaluation efficiently by generating program defect information, needed to execute sensitivity evaluation of the reticle inspection apparatus, on that CAD data which is input to the reticle inspection apparatus, not on a real reticle.
2. Description of the Related Art
Conventional defect inspection apparatuses for use in the semiconductor fabrication process generally employ an inspection scheme of comparing the characteristics of an image generated based on design data called CAD data with the characteristics of a real image and detecting difference as defects (flaw points).
Such a defect inspection apparatus uses a sample in which defects are intentionally programmed for the purpose of objectively evaluating the performance of the apparatus. This sample is called a sample with program defects. To measure the performance of the defect inspection apparatus, a sample is programmed with defects of various characteristic types and sizes. For example, one sample has ten types of defects and twenty different sizes for each type from a small defect to a large one. The defect inspection apparatus inspects the sample and its performance is evaluated by the level of difficulty of a defect which it can detect. The evaluation process is generally called “sensitivity evaluation”.
The operation of executing the conventional sensitivity evaluation process is described below referring to FIGS. 1 and 2. The broken-lined blocks in FIG. 2 are procedures that are carried out manually or so, not procedures that are executed by a data processing unit 200.
First, to execute sensitivity evaluation, a reticle 500 programmed with the program defect information is prepared separate from a normal reticle for inspection. A “reticle” is a photomask which is used in exposing a circuit pattern on a wafer in the fabrication process for a semiconductor device. Preparation of the reticle 500 requires source CAD data 100 having program defect information (step S103 in FIG. 2). The source CAD data 100 is hereinafter referred to as “program-defect-information-present source CAD data 100”.
As a comparison target is prepared source CAD data 301 that is the program-defect-information-present source CAD data 100 from which the program defect information is removed (step S104 in FIG. 2). The source CAD data 301 is hereinafter referred to as “program-defect-information-free source CAD data 301”.
To execute normal inspection, by way of contrast, a reticle having no program defects (hereinafter referred to as “program-defect-information-free reticle”) and its source CAD data are prepared (step S102 in FIG. 2). This requires to design whether to execute normal inspection or sensitivity evaluation prior to the fabrication of the reticle (step S101 in FIG. 2).
The prepared CAD data, regardless of whether it is used in normal inspection or sensitivity evaluation, is converted to data 302, which can be input to the reticle inspection apparatus and is in turn output (steps S105 and S106 in FIG. 2).
Techniques relating to the reticle inspection apparatus that is used in the conventional semiconductor fabrication process or so include one which can inspect the outer appearance of a photomask under the same conditions as involved in actual exposure of a photomask on a wafer by a stepper (see, for example, Japanese Patent Laid-Open Publication No. 2000-258349) and one which can easily set parameters for the defect inspection apparatus (see, for example, Japanese Patent Laid-Open Publication No. 2002-048722).
The execution of the conventional sensitivity evaluation however has the following problems that cannot be overcome by the conventional defect inspection apparatus.
The first problem of the conventional sensitivity evaluation is an extreme difficulty in programming defects of a small size which are worth evaluating. The micronization of semiconductor design rules demands that the defect inspection apparatus should detect smaller defects. Evaluation of state-of-the-art inspection apparatuses demands that the size of program defects should be small enough to be able to evaluate the optimal performance. The smaller the size is, the harder it becomes to accurately program defects, so that defects of a desirable size for evaluation are not often obtained.
The second problem is that a work of measuring the sizes of programmed defects takes considerable time and labor, making it difficult to acquired objective measurements. To properly evaluate the performance of the defect inspection apparatus, it is necessary to accurately identify the sizes of detected defects. The smaller the size of a program defect is, however, the more likely it is to cause a factitious fluctuation in measurements. Unless measurements are taken in the right environment under the precise decision conditions, objective defects-programmed samples cannot be obtained. This requires a high level of measuring technique and sophisticated environment, and the time required for the measuring task becomes longer every year.
The third problem is that the diversification of semiconductor design makes it necessary to prepare a lot of reticles having various kinds of defect information different from one another in the characteristics of program defects to be evaluated. This problem, like the first problem, leads to the difficulty in acquiring samples with accurately programmed defects. An increase in the types of program defects means an increase in the number of defects to be measured, which leads to the second problem.
The fourth problem is that the diversification of semiconductor design diversifies the characteristics of the background where defects are placed as well as the types of the characteristics of defects themselves. A defect-programmed sample is exclusive for sensitivity evaluation and cannot be used as a product. This makes it substantially difficult to prepare fabrications of different types that cover the variation of products.
The fifth problem lies in the necessity to prepare two kinds of CAD data, namely CAD data for fabricating a defect-programmed sample and CAD data having no program defect information for sensitivity evaluation. In sensitivity evaluation, the real image of a defect-present sample should be compared with an image generated from CAD data having no defect information to detect differences. A process up to the execution of sensitivity evaluation requires longer time than the normal inspection process by the time needed to prepare data.